[LowerTypeTests] Discard extern_weak linkage for definitions

Summary:
Fix PR37625. It's possible for an extern_weak declaration to be emitted
to the merged module when a definition exists in the ThinLTO portion of
the build; discard the linkage on the declaration in that case.
(otherwise we copy the linkage to the alias to the jumptable and fail)

Reviewers: pcc

Reviewed By: pcc

Subscribers: mehdi_amini, llvm-commits, kcc

Differential Revision: https://reviews.llvm.org/D47494

llvm-svn: 333604

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index d2545af8502..1e4d3d37aae 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1716,6 +1716,11 @@ bool LowerTypeTestsModule::lower() {
           F->clearMetadata();
         }
 
+        // Update the linkage for extern_weak declarations when a definition
+        // exists.
+        if (Linkage == CFL_Definition && F->hasExternalWeakLinkage())
+          F->setLinkage(GlobalValue::ExternalLinkage);
+
         // If the function in the full LTO module is a declaration, replace its
         // type metadata with the type metadata we found in cfi.functions. That
         // metadata is presumed to be more accurate than the metadata attached